Can spread operator solve below problem? Imagine I have more fields, then I have to declare req.body.something for every single fields, that's so tedious.
app.use((res,req,next) => {
const obj = {
name: req.body.name,
age: req.body.age,
gender: req.body.gender
}
//
User.saveUser(resp => res.json(resp)) //User model
})
You can use destructuring assignment:
const obj = req.body;
const { name, age, gender } = obj;
But, still you will have to validate it, and count all of them in your scheme.
Update:
Adding some validation example.
Assuming such schema in your route:
const tv4 = require('tv4');
const schema = {
type: 'object',
properties: {
name: 'string',
age: number,
gender: {
type: 'string',
pattern: /f|m/i
}
},
required: ['name']
};
And then, in your handler you validate:
if (tv4.validate(req.body, schema) {
// continue your logic here
} else {
// return 400 status here
}
You can use lodash's pick():
_.pick(object, [paths])
Creates an object composed of the picked object properties.
Example code is:
const _ = require('lodash');
...
const obj = _.pick(req.body, ['name', 'age', 'gender']);
If gender does not exist in req.body, it would be ignored -- the result obj object won't have a gender field.
If all the req.body fields are needed, you can just assign req.body to obj:
const obj = req.body;
To validate req.body content, you can use lodash's .has():
_.has(object, path)
Checks if path is a direct property of object.
Example code would be:
_.has(req.body, ['name', 'age', 'gender']); // return true if all fields exist.
You can use destructuring assignment
const { name, age, gender } = req.body
or if you wanna use spread operation, you can use :
const obj = { ...req.body }
Hope it helps!
Related
Let's suppose I have the following object:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
And that I want only the id and fullName.
I will do the following :
const { id, fullName } = user
Easy-peasy, right?
Now let's suppose that I want to do the destructuring based on the value of another variable called fields.
const fields = [ 'id', 'fullName' ]
Now my question is : How can I do destructuring based on an array of keys?
I shamelessly tried the following without success:
let {[{...fields}]} = user and let {[...fields]} = user. Is there any way that this could be done?
Thank you
It's not impossible to destructure with a dynamic key. To prevent the problem of creating dynamic variables (as Ginden mentioned) you need to provide aliases.
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName' ];
const object = {};
const {[fields[0]]: id, [fields[1]]: fullName} = user;
console.log(id); // 42
console.log(fullName); // { firstName: "John", lastName: "Doe" }
To get around the problem of having to define static aliases for dynamic values, you can assign to an object's dynamic properties. In this simple example, this is the same as reverting the whole destructuring, though :)
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName' ];
const object = {};
({[fields[0]]: object[fields[0]], [fields[1]]: object[fields[1]]} = user);
console.log(object.id); // 42
console.log(object.fullName); // { firstName: "John", lastName: "Doe" }
sources:
https://twitter.com/ydkjs/status/699845396084846592
https://github.com/getify/You-Dont-Know-JS/blob/master/es6%20%26%20beyond/ch2.md#not-just-declarations
Paul Kögel's answer is great, but I wanted to give a simpler example for when you need only the value of a dynamic field but don't need to assign it to a dynamic key.
let obj = {x: 3, y: 6};
let dynamicField = 'x';
let {[dynamicField]: value} = obj;
console.log(value);
Short answer: it's impossible and it won't be possible.
Reasoning behind this: it would introduce new dynamically named variables into block scope, effectively being dynamic eval, thus disabling any performance optimization. Dynamic eval that can modify scope in fly was always regarded as extremely dangerous and was removed from ES5 strict mode.
Moreover, it would be a code smell - referencing undefined variables throws ReferenceError, so you would need more boilerplate code to safely handle such dynamic scope.
As discussed before, you can't destruct into dynamically named variables in JavaScript without using eval.
But you can get a subset of the object dynamically, using reduce function as follows:
const destruct = (obj, ...keys) =>
keys.reduce((a, c) => ({ ...a, [c]: obj[c] }), {});
const object = {
color: 'red',
size: 'big',
amount: 10,
};
const subset1 = destruct(object, 'color');
const subset2 = destruct(object, 'color', 'amount', 'size');
console.log(subset1);
console.log(subset2);
You can't destruct without knowing the name of the keys or using an alias for named variables
// you know the name of the keys
const { id, fullName } = user;
// use an alias for named variables
const { [fields[0]]: id, [fields[1]]: fullName } = user;
A solution is to use Array.reduce() to create an object with the dynamic keys like this:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName', 'age' ];
const obj = fields.reduce((acc, k) => ({ ...acc, ...(user.hasOwnProperty(k) && { [k]: user[k] }) }), {});
for(let k in obj) {
console.log(k, obj[k]);
}
I believe that the above answers are intellectual and valid because all are given by pro developers. :). But, I have found a small and effective solution to destructure any objects dynamically. you can destructure them in two ways. But both ways are has done the same action.
Ex:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
using "Object.key", "forEach" and "window" object.
Object.keys(user).forEach(l=>window[l]=user[l]);
Simply using Object. assign method.
Object.assign(window, user)
Output:
console.log(id, displayName, fullName)
// 42 jdoe {firstName: "John", lastName: "Doe"}
Anyway, I am a newbie in JS. So, don't take it as an offense if you found any misleading info in my answer.
I have this code:
let peopleInRoom = [];
for (let message of messages) {
for (let email of message.user.email) {
if (!peopleInRoom.includes(email)) {
peopleInRoom.push(email);
}
}
}
let peopleInRoomElement = peopleInRoom.map(person => (
<li>{person}</li>
))
Basically I am trying to get all the unique emails and display them.
Is there a shorter and more efficient way (maybe some ES6 features) to write the same code? Seems too much code than needed.
I looked at this answer: How to get distinct values from an array of objects in JavaScript?
EDIT: Above code does not do what I want.
My data looks like this:
[
{
text: 'foo',
user: { email: 'foo#bar.com', password: 'foo' }
},
{
text: 'baz',
user: { email: 'baz#qux.com', password: 'baz' }
}
]
The objects are all messages. And I want to get an array of all the unique emails from each message
You can use the Set object that is built into JavaScript. Set object actually keep the distinct primitive values.
const messages = [
{
text: 'foo',
user: { email: 'foo#bar.com', password: 'foo' }
},
{
text: 'baz',
user: { email: 'baz#qux.com', password: 'baz' }
}
]
const peopleInRoom = [...new Set(messages.map(message => message.user.email))];
It actually extracts the email from each message and then passes it to the Set object which only keeps the unique set of emails. After that, it will spread that Set to the array, since Set is also an iterable and returns the array of the people in room.
If I understand correctly, people have messages, messages have email addresses and the OP seeks the unique set of email addresses. If that's all the data available, then there's no alternative but to iterate it, checking to see if each email has been collected already, and collecting it if it hasn't been.
There are ways to conceal this work by doing it in library code. Probably the highest level utility is lodash's _.uniqueBy, but the work must be done one way or another.
The Set object enforces uniqueness of its elements. You can use it this way:
const peopleInRoom = Array.from(new Set(messages.map(message => message.user.email)));
First you can make an array of all the email addresses:
const data = [
{
text: 'foo',
user: { email: 'foo#bar.com', password: 'foo' }
},
{
text: 'baz',
user: { email: 'baz#qux.com', password: 'baz' }
}
]
const emailArray = data.map((elem) => {
return elem.user.email;
}
and then you can filter them to be unique:
function onlyUnique(value, index, self) {
return self.indexOf(value) === index;
}
emailArrayFiltered = emailArray.filter(onlyUnique);
see here for ref link
What about:
const peopleInRoom = messages.map(e => e.user.email && e.user.email);
console.log(peopleInRoom)
gives you this output:
["foo#bar.com", "baz#qux.com"]
I have object which I want to validate.
// valid object because all values of keys are present in details object
var object = {
details: {
key1: 'stringValue1',
key2: 'stringValue2',
key3: 'stringValue3'
},
keys: ['key1', 'key2', 'key3']
}
// invalid object as key5 is not present in details
var object = {
details: {
key4: 'stringValue4'
},
keys: ['key4', 'key5']
}
// invalid object as key5 is not present and key8 should not exist in details
var object = {
details: {
key4: 'stringValue4',
key8: 'stringValue8',
},
keys: ['key4', 'key5']
}
All the keys present in keys should be present in details also.
I tried this using Joi.ref()
var schema = Joi.object({
details: Joi.object().keys(Object.assign({}, ...Object.entries({...Joi.ref('keys')}).map(([a,b]) => ({ [b]: Joi.string() })))),
keys: Joi.array()
})
But this is not working because Joi.ref('keys') will get resolved at validation time.
How can I validate this object using Joi?
Using object.pattern and array.length
var schema = Joi.object({
details: Joi.object().pattern(Joi.in('keys'), Joi.string()),
keys: Joi.array().length(Joi.ref('details', {
adjust: (value) => Object.keys(value).length
}))
});
stackblitz
You can validate the array(if you want) then make a dynamic schema and validate that.
const arrSchema = Joi.object({
keys: Joi.array()
});
then,
const newSchema = Joi.object({
details: Joi.object().keys(data.keys.reduce((p, k) => {
p[k] = Joi.string().required();
return p;
},{})),
keys: Joi.array()
})
This should probably do it.
You have to set allowUnknown: true in validate() option.
Let's suppose I have the following object:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
And that I want only the id and fullName.
I will do the following :
const { id, fullName } = user
Easy-peasy, right?
Now let's suppose that I want to do the destructuring based on the value of another variable called fields.
const fields = [ 'id', 'fullName' ]
Now my question is : How can I do destructuring based on an array of keys?
I shamelessly tried the following without success:
let {[{...fields}]} = user and let {[...fields]} = user. Is there any way that this could be done?
Thank you
It's not impossible to destructure with a dynamic key. To prevent the problem of creating dynamic variables (as Ginden mentioned) you need to provide aliases.
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName' ];
const object = {};
const {[fields[0]]: id, [fields[1]]: fullName} = user;
console.log(id); // 42
console.log(fullName); // { firstName: "John", lastName: "Doe" }
To get around the problem of having to define static aliases for dynamic values, you can assign to an object's dynamic properties. In this simple example, this is the same as reverting the whole destructuring, though :)
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName' ];
const object = {};
({[fields[0]]: object[fields[0]], [fields[1]]: object[fields[1]]} = user);
console.log(object.id); // 42
console.log(object.fullName); // { firstName: "John", lastName: "Doe" }
sources:
https://twitter.com/ydkjs/status/699845396084846592
https://github.com/getify/You-Dont-Know-JS/blob/master/es6%20%26%20beyond/ch2.md#not-just-declarations
Paul Kögel's answer is great, but I wanted to give a simpler example for when you need only the value of a dynamic field but don't need to assign it to a dynamic key.
let obj = {x: 3, y: 6};
let dynamicField = 'x';
let {[dynamicField]: value} = obj;
console.log(value);
Short answer: it's impossible and it won't be possible.
Reasoning behind this: it would introduce new dynamically named variables into block scope, effectively being dynamic eval, thus disabling any performance optimization. Dynamic eval that can modify scope in fly was always regarded as extremely dangerous and was removed from ES5 strict mode.
Moreover, it would be a code smell - referencing undefined variables throws ReferenceError, so you would need more boilerplate code to safely handle such dynamic scope.
As discussed before, you can't destruct into dynamically named variables in JavaScript without using eval.
But you can get a subset of the object dynamically, using reduce function as follows:
const destruct = (obj, ...keys) =>
keys.reduce((a, c) => ({ ...a, [c]: obj[c] }), {});
const object = {
color: 'red',
size: 'big',
amount: 10,
};
const subset1 = destruct(object, 'color');
const subset2 = destruct(object, 'color', 'amount', 'size');
console.log(subset1);
console.log(subset2);
You can't destruct without knowing the name of the keys or using an alias for named variables
// you know the name of the keys
const { id, fullName } = user;
// use an alias for named variables
const { [fields[0]]: id, [fields[1]]: fullName } = user;
A solution is to use Array.reduce() to create an object with the dynamic keys like this:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
const fields = [ 'id', 'fullName', 'age' ];
const obj = fields.reduce((acc, k) => ({ ...acc, ...(user.hasOwnProperty(k) && { [k]: user[k] }) }), {});
for(let k in obj) {
console.log(k, obj[k]);
}
I believe that the above answers are intellectual and valid because all are given by pro developers. :). But, I have found a small and effective solution to destructure any objects dynamically. you can destructure them in two ways. But both ways are has done the same action.
Ex:
const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};
using "Object.key", "forEach" and "window" object.
Object.keys(user).forEach(l=>window[l]=user[l]);
Simply using Object. assign method.
Object.assign(window, user)
Output:
console.log(id, displayName, fullName)
// 42 jdoe {firstName: "John", lastName: "Doe"}
Anyway, I am a newbie in JS. So, don't take it as an offense if you found any misleading info in my answer.
Currently, when I want to prune an object (say, a user object that has details I don't want to send to the client), I have been copying over properties like so:
let user = db.findUser(_id);
//user = { username: "John", hashedPassword: "ashHDhadh23hfJAd", email: "John#doe.com", created: "<some date>" ... }
let forClient = {
username: user.username,
email: user.email
}
...
I am learning about destructuring an object in ES2015 and it seems like it might be possible to do this more cleanly. Is it?
Destructuring won't help here without introducing overhead. It simplifies creating variables from an object, i.e. if you would use it here, it result in something like this:
let { username, email } = user;
let forClient = { username, email };
But as you can see, this adds new variables and repeats code.
You could consider using reduce to select the wanted fields:
let forClient = ['username', 'email'].reduce((v, k) => { v[k] = user[k]; return v }, {});
... or with a higher-order function to not repeat too much code:
const selectFrom = (obj) => (v, k) => { v[k] = obj[k]; return v };
let userForClient = ['username', 'email'].reduce(selectFrom(user), {});
let postForClient = ['title', 'summary'].reduce(selectFrom(blogpost), {});
// etc.
... or just add a function like this to your library, which uses the rest spread operator for simple usage:
function pruneObject(obj, ...fields) {
let pruned = {};
fields.forEach(f => pruned[f] = obj[f]);
return pruned;
}
let forClient = pruneObject(user, 'username', 'email');